Detecting and counting bacteria suspended in a biological fluid by means of light scattering measurements is known. In US patent application 20070211251A1, which is incorporated herein by reference, a system and method for detecting and measuring the concentration of bacteria suspended in biological fluids, such as urine, by means of light scattering measurements are disclosed. The disclosed system includes cuvettes whose windows have any of the following feature: their refractive index is homogeneous, such that deviations of its values do not exceed 10−4, the root mean square of the changes in the surface roughness of the windows do not exceed 1 nanometer, the scratch/dig number associated with the surfaces of the windows does not exceed 40/20, and/or the widths of the windows do not exceed 500 micrometer (μm). The disclosed cuvettes are adapted to contain a sample of the biological fluid to be tested for the presence of bacteria by means of collimated light beam. The intensity of the scattered light is associated with a scattering profile to which is further compared to standard scattering profiles serving as a calibration scale. A set of standard scattering profiles comprises scattering profiles and linear combination of scattering profiles which were measured for suitable numbers of bacterial suspensions whose concentrations are known and further ensemble averaged.
Light scattering measurements are prone to errors at low concentrations of scatterers, such as of 104 colony forming units per milliliter (CFU/ml) or lower levels. Therefore any system and method providing for relatively high sensitivity and specificity especially considering such low concentrations are beneficial.